Active fixation medical lead

ABSTRACT

An implantable medical device that includes an elongated body having a proximal end and a distal end, a helical fixation member extending from the distal end of the elongated body, the helical fixation member including a distal tip for affixing the distal end of the elongated body at an implant site, and a tracking member extending from the distal end of the elongated body, through the helical fixation member and outward from the distal tip of the helical fixation member for tracking along an implant pathway during implantation of the implantable medical device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/186,551 filed on Jul. 21, 2005, now issued as U.S. Pat. No. 7,532,939on May 12, 2009. The disclosure of the above application is incorporatedherein by reference.

TECHNICAL FIELD

The invention relates to implantable medical devices, particularly toconfigurations of elongated medical devices facilitating deployment toand fixation at an implant site.

BACKGROUND

In the medical field, implantable elongated medical devices, such asleads and catheters, are used with a wide variety of therapeutic ormonitoring devices. For example, implantable leads are commonly used toform part of implantable cardiac pacemaker systems that providetherapeutic stimulation to the heart by sensing electrical activity ofthe heart and delivering pacing, cardioversion, or defibrillation pulsesvia electrodes disposed on the leads, typically near the distal ends ofthe leads. Elongated medical devices may also be used to delivertherapeutic agents. A number of challenges exist with respect to suchmedical devices, in particular, as more advanced and complex therapeutictechniques are developed, new configurations are required to facilitatedeployment and fixation of elongated medical devices at targeted implantsites within a patient.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects and features of the present invention will be readilyappreciated as the same becomes better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings, in which like reference numerals designate likeparts throughout the figures thereof and wherein:

FIG. 1 is a schematic diagram of an implantable medical device accordingto an embodiment of the present invention;

FIG. 2 is a plan view of an elongated medical device according to anembodiment of the present invention;

FIG. 3 is an end view of the elongated device shown in FIG. 2;

FIG. 4A is a schematic diagram of a distal end of an elongated medicaldevice implanted in a blood vessel according to an embodiment of thepresent invention;

FIG. 4B is a schematic diagram of the engagement of implant-site tissuebetween a helical fixation member and a tracking member extending from adistal end of an elongated medical device, according to an embodiment ofthe present invention;

FIG. 5 is a sectional view of the distal end of the elongated medicaldevice shown in FIG. 2, which illustrates one configuration of a helicalfixation member and a tracking member;

FIG. 6 is a schematic diagram of a helical fixation member and atracking member according to an embodiment of the present invention;

FIG. 7A is an end view of an elongated medical device illustrating oneconfiguration of the tissue-piercing distal tip of the helical fixationmember;

FIG. 7B is an end view of a tracking member having a non-circularcross-section resulting in a non-uniform tissue-engaging space betweenthe tracking member and the helical fixation member;

FIG. 8 is a schematic diagram of a helical fixation member andcorresponding tracking member according to an embodiment of the presentinvention;

FIG. 9 is a schematic diagram of a helical fixation member and trackingmember according to yet another embodiment;

FIG. 10 is a schematic diagram of a tracking member having a fixed outerdiameter along a proximal portion and a tapering or decreasing diameteralong a distal portion according to an embodiment of the presentinvention;

FIG. 11 is a plan view of a medical electrical lead according to anembodiment of the present invention;

FIG. 12 illustrates a method for deploying an elongated medical devicein accordance with an embodiment of the present invention;

FIG. 13A is an enlarged view of an elongated medical device beingadvanced into a cardiac vein over guide wire according to an embodimentof the present invention;

FIG. 13B illustrates fixation of a elongated medical device at thetargeted implant site in vein according to an embodiment of the presentinvention;

FIG. 14 is a plan view of a stylet that may be used in combination withan elongated medical device according to an embodiment of the presentinvention;

FIG. 15A is a sectional view of an elongated medical device showing astylet fully inserted in the device according to an embodiment of thepresent invention;

FIG. 15B is a sectional view of a distal portion of an elongated medicaldevice provided with a solid tracking member according to an embodimentof the present invention; and

FIG. 16 is a sectional view of an elongated medical device and amicrocatheter extending there through for use in local administration ofa fluid agent according to an embodiment of the present invention;

DETAILED DESCRIPTION

The following detailed description provides a practical illustration forimplementing various embodiments of the invention and is not intended tolimit the scope, applicability, or configuration of the invention in anyway.

FIG. 1 is a schematic diagram of an implantable medical device accordingto an embodiment of the present invention. As illustrated in FIG. 1, amimplantable medical device 10 according to an embodiment of the presentinvention includes a cardiac therapy/monitoring device housing 12 and alead 14, shown coupled to housing 12. Lead 14 is provided with a distalend 16, configured to facilitate fixation within a blood vessel at atargeted implant site so that a therapy can be delivered through lead 14to a heart 7 from housing 12. Housing 12 includes circuitry for enablingdevice 10 to be capable of delivering pacing, cardioversion and/ordefibrillation therapy to a patient via electrodes disposed on lead 14.As such, housing 12 includes a therapy delivery module 11 which includesthe electrical circuitry to generate stimulation pulses and control thetiming and delivery of electrical stimulation pulses. Such circuitry iswell known in the art of cardiac pacemakers. Housing 12 further includesmonitoring module 13 for monitoring physiological signals received bylead 14, and may further include switching circuitry 9 for facilitatingselection of various electrodes available on lead 14 for sensing cardiacsignals and/or for delivering stimulation therapy. Electrode-selectingswitching circuitry is known in the art.

Embodiments of the present invention are not limited for use inelectrical stimulation therapy delivery. Therapy delivery module mayalternatively or additionally include a drug pump for administering apharmaceutical, biologic or genetic agent. As such, lead 14 may includea fluid delivery lumen coupled to therapy/monitoring device 12. Lead 14may additionally or alternatively include physiological sensors forgathering physiological data for patient monitoring purposes bymonitoring module 13. Devices that integrate monitoring and therapydelivery features, along with connection means for associated leads, arewell known to those skilled in the art.

As illustrated in FIG. 1, lead 14 is used as a coronary sinus lead,implanted in a cardiac vein 8 via the coronary sinus and fixed at acorresponding left ventricular epicardial site 6 of the heart 7. As usedherein “coronary sinus lead” refers to a lead implanted in the cardiacvasculature via the coronary sinus, which can include any cardiac veinbranch. According to embodiments of the present invention, distal end 16of lead 14 includes a fixation element and tracking member extendingtherefrom, to facilitate deployment of lead 14 and fixation at theillustrated implant site. Distal end 16, as will be illustrated by thevarious embodiments described herein, is configured to allow fixation ofan elongated medical device, such as the coronary sinus lead 14 shown inFIG. 1 or other leads or catheters, within a generally tubular organsuch as a blood vessel. Implant sites made more viable by embodiments ofthe present invention include those accessed by implantation of anelongated medical device in any cardiac vein. Furthermore, embodimentsof the present invention are not limited to cardiac or vascularimplantation sites but may also find use in other locations in a body,for example for neuro-stimulation or drug or biological fluid delivery.

FIG. 2 is a plan view of an elongated medical device according to anembodiment of the present invention. As illustrated in FIG. 2, accordingto an embodiment of the present invention, an elongated medical device20, which may be embodied as the coronary sinus lead 14 shown in FIG. 1,includes an elongated body 22 having at least one lumen 23 extendingbetween a proximal end 24 and a distal end 26 of elongated body 22.Proximal end 24 may be provided with a connector assembly 28 for use incoupling elongated device 20 to an implantable monitoring/therapydelivery device. For example, elongated device 20 may be electricallycoupled to a cardiac stimulation device, such as a pacemaker orcardioverter/defibrillator. In alternative embodiments, proximal end 24of elongated device 20 may be configured for connection to a drug pump,neuro-stimulator, or other monitoring or therapy delivery device.

A helical fixation member 32 is provided extending from the distal end26 of elongated body 22. Helical fixation member 32 is adapted foractively fixing the distal end 26 of elongated device 20 at a desiredimplant site. As such, helical fixation member 32 is provided with atissue-piercing distal tip 34.

A tracking member 30 also extends from the distal end 26 of elongatedbody 22, with helical fixation member 32 extending about tracking member30 so that tracking member 30 extends through helical fixation member 32with a distal end of tracking member 30 extending distally outward fromtissue-piercing distal tip 34. The distance that tracking member 30extends outward form tissue-piercing distal tip 34 can vary betweenembodiments and could range, for example, from a fraction of acentimeter to several centimeters. Tracking member 30 facilitatestracking of elongated medical device distal end 26 along an implantpathway and is therefore referred to herein as a “tracking member” forthe sake of convenience. However, tracking member 30 can also serveother functions as will become apparent from the following descriptionand is not limited to performing tracking functions per se. For example,tracking member 30 also acts to prevent catching or snagging oftissue-piercing distal tip 34 on body tissue or anatomical featuresduring advancement of elongated medical device 20 to an implant site.

FIG. 3 is an end view of elongated device 20. Another function oftracking member 30 is to cooperate with helical fixation member 32 toengage tissue between fixation member 32 and tracking member 30 uponrotation of fixation member 32 within body tissue during fixation ofhelical member 32 at an implant site. As such, at least a portion of thedistal windings of helical fixation member 32 are proportioned relativeto the adjacent outer surface of tracking member 30 so that fixationmember 32 is positioned a distance 36 from tracking member 30 to form agap between fixation member 32 and tracking member 30. Body tissue atthe implant site becomes engaged or “sandwiched” within the gap betweenhelical fixation member 32 and tracking member 30 when helical fixationmember 32 is rotated into the body tissue at the implant site to fixdistal end 26 of elongated medical device 20.

Distance 36 that fixation member 32 is spaced from tracking member 30controls the depth that helical fixation member 32 penetrates into thebody tissue at the implant site. The length of distance 36 betweenfixation member 32 and tracking member 30, as well as the lineardistance along tracking member 30 that distance 36 extends will varybetween embodiments and will depend on various design considerationssuch as the anatomical location and type of tissue in which helicalfixation member 32 is implanted and other relative dimensions offixation member 32 and tracking member 30. Distance 36 may range insize, for example, from approximately 0.005 inches to approximately 0.02inches, but is not limited to this range. According to an embodiment ofthe present invention, fixation member 32 is spaced distance 36 fromtracking member 30 along the entire length of fixation member 32.However, according to another embodiment of the present invention,fixation member 32 is spaced distance 36 from tracking member 30 alongonly a distal portion of fixation member 32, with the outer diameter oftracking member 30 being approximately equal to the inner diameter offixation member 32 (i.e., distance 36 is approximately zero) along aproximal portion of fixation member 32. The linear distance that space36 extends along the distal portion of helical fixation member 32 mayrange from approximately one millimeter to several centimeters,depending on the overall length of helical fixation member 32 and theparticular application.

In the example of the coronary sinus lead embodiment of FIG. 1, helicalfixation member 32 may be provided having a 4 French diameter withtracking member having an outer dimension of approximately 0.04 inchesso that distance 36 between tracking member 30 and fixation member 32 isapproximately 0.01 inches. Helical fixation member 32 and correspondingtracking member 30 may be provided with different diameters for use incardiac veins of different sizes. Distance 36 may extend, for example,for approximately 0.25 cm to approximately 1 cm along a linear distanceof the distal portion of helical fixation member 32 included in acoronary sinus lead.

FIG. 4A is a schematic diagram of a distal end of an elongated medicaldevice implanted in a blood vessel according to an embodiment of thepresent invention. FIG. 4B is a schematic diagram of the engagement ofimplant-site tissue between a helical fixation member and a trackingmember extending from a distal end of an elongated medical device,according to an embodiment of the present invention. FIGS. 4A and 4Billustrate the engagement of implant-site tissue between helicalfixation member 32 and tracking member 30 according to an embodiment ofthe present invention. In FIG. 4A, the distal end 26 of elongatedmedical device 20 is shown implanted in a blood vessel 15. In someapplications, blood vessel 15 is a cardiac vein. Distal winding 35 ofhelical fixation member 32 is shown having an inner diameter greaterthan the outer diameter of tracking member 30 such distal winding 35 isspaced distance 36 from tracking member 30. Elongated device body 22 isprovided with adequate torsional stiffness so as to translate rotationalmovement applied at its proximal end to the distal end 26 to therebycause rotation of helical fixation member 32. As elongated medicaldevice 20 is advanced along an implant pathway, body 22 may becounter-rotated (i.e., rotated in a direction opposite that required toaffix helical fixation member in tissue) to prevent tissue-piercingdistal tip 34 from catching or snagging on body tissue or anatomicalfeatures.

When tracking member 30 is positioned at a desired implant site,elongated medical device 20 is rotated at its proximal end by theimplanting clinician, causing tissue-piercing distal tip 34 of helicalfixation member 32 to pierce into blood vessel 15. In the example shown,distal tip 34 penetrates through the wall of blood vessel 15 at site 18.In a cardiac vein application, distal tip 34 may penetrate through thewall of vessel 15 into surrounding myocardial tissue. In practice,distal tip 34 may pierce into a targeted blood vessel wall, or any otherbody tissue at the fixation site, with or without fully penetratingthrough the tissue, depending on the tissue thickness and relative sizeof helical fixation member 32 and tracking member 30 and thecorresponding tissue-engaging space 36 formed there between.

As shown in FIG. 4B, further rotation of elongated device 20 causeshelical fixation member 32 to advance through piercing site 18 such thata segment 19 of blood vessel 15 becomes engaged in the gap formed bydistance 36 between helical fixation member 32 and tracking member 30.Distance 36 between tracking member 30 and helical fixation member 32for engaging implant-site tissue between helical fixation member 32 andtracking member 30 is provided linearly along all or at least a portionof helical fixation member windings, extending proximally fromtissue-piercing distal tip 34, by forming at least a portion of thewindings with a larger diameter than the adjacent outer diameter 37 oftracking sleeve 30.

As illustrated in FIGS. 4A and 4B, the diameter of the inner surface ofhelical fixation member 32 is approximately equal to the diameter oftracking member 30 along proximal winding 33 of helical fixation member32 so that there is no longer a gap formed by distance 36 along proximalwinding 33. In this way, proximal winding 33 acts as a mechanical stopagainst further advancement of fixation member 32 into vessel 15. Astissue engaged within gap form by distance 36 reaches proximal winding33, further proximal advancement of tissue between helical fixationmember 32 and tracking member 30 is inhibited, resulting in greaterresistance being met with further rotation of elongated device 20.Torque is built up on elongated device body 22 providing tactilefeedback to the clinician that the distal end 26 is fixed. The torsionalstiffness of elongated device body 22 is designed to provide translationof rotational movement from the proximal end to distal end 26 of device20 during advancement and fixation of distal end 26 and to providetactile feedback of torque build-up when helical fixation member isfully fixed in body tissue at the implant site. In one embodiment,elongated device body 22 is formed from 55D polyurethane, however, otherdurometer materials may provide acceptable torsional stiffness fortranslating proximal to distal rotational motion and distal to proximaltorque feedback.

By providing of tracking member 30 extending through helical fixationmember 32, and spaced distance 36 from helical fixation member 32 alongat least the distal portion 35 of the windings so that tissue isadvanced between helical fixation member 32 and tracking member 30during rotation of the elongated device 20 promotes parallel orsubstantially concentric tracking of the blood vessel 15 by helicalfixation member 32 during fixation of member 32 to control the depth ofpenetration within the surrounding tissue by helical fixation member 32.In cardiac vein applications, limiting the position of the helicalfixation member 32 to within or proximate the vein wall reduces thelikelihood of inadvertently piercing a nearby artery during fixation ofmember 32.

FIG. 5 is a sectional view of the distal end of elongated medical device20, which illustrates one configuration of a helical fixation member anda tracking member. Helical fixation member 32 is shown having a fixedwinding diameter 40 greater than the outer diameter 42 of trackingmember 30 so that tracking member 30 is spaced distance 36 from helicalfixation member 32 for the entire length of helical fixation member thatextends from distal end 26 of elongated body 22. Tracking member 30 canbe formed as a molded component, typically fabricated from a polymermaterial such as silicone or polyurethane.

As illustrated in FIG. 5, according to an embodiment of the presentinvention, tracking member 30 is fixed to a welding sleeve 44 used inassembling elongated medical device 20. Welding sleeve 44 is adhesivebonded or otherwise fixed within elongated medical device body 22, neardistal end 26. Welding sleeve 44 is shown having a channel 46 on itsinner diameter to accommodate tracking member 30. Tracking member 30 maybe molded into welding sleeve 44 or compression fit and/or adhesivebonded to welding sleeve 44. Tracking member 30 is thereby fixedlycoupled to elongated medical device body 22 via welding sleeve 44.

Helical fixation member 32 is welded to the outer diameter of weldingsleeve 44. In some embodiments, helical fixation member 32 functionsadditionally as an electrode for sensing electrical body signals or fordelivering an electrical stimulation therapy. As such, helical fixationmember 32 is formed of a conductive material, such as platinum, iridium,a platinum-iridium alloy, stainless steel or other material known foruse in fabricating implantable electrodes. Welding sleeve 44 is likewiseformed from a conductive material and provides electrical couplingbetween helical fixation member 32 and a conductor 50, shown in FIG. 5as a coiled conductor. Conductor 50 extends from welding sleeve 44 tothe proximal end of elongated medical device 20 through lumen 23 whereit is coupled to a connecter assembly according to methods known in theart.

According to an embodiment of the present invention, tracking member 30may be adhesively bonded directly to the elongated body 22. If helicalfixation member 32 is not intended for use as an electrode, weldingsleeve 44 is not required for providing electrical coupling of fixationmember 32 to a conductor. As such, a configuration of distal end 26 mayinclude helical fixation member 32 and tracking member 30 bonded todistal end 26 without the use of welding sleeve 44.

Tracking member 30 is shown as a hollow member having an open lumen 54.Elongated body 22 is provided with a lumen 23 that is in communicationwith tracking member lumen 54. Tracking member 30 includes a distalopening 56 to enable an elongated member or fluid agent to be passedthrough elongated body lumen 23, tracking member lumen 54 and out distalend 38 of tracking member 30. As will be described in greater detailbelow, elongated medical device 20 may be deployed over a guide wire toa desired implant site. A previously placed guide wire can pass throughopening 38 as elongated device 20 is advanced over the guide wire to atargeted implant site.

In certain embodiments, elongated medical device 20 may be used as afluid delivery catheter or in conjunction with a drug pump for localadministration of a biological, pharmacological, or genetic material ina fluid agent. The fluid agent may be delivered through body lumen 23and tracking member lumen 54 through opening 56 into the surroundingbody tissue and/or fluids. A micro-catheter or needle used foradministering the fluid agent may be passed through body lumen 23,tracking member lumen 54 and out tracking member distal end 38 throughopening 56. It is recognized that tracking member 30 may be providedwith multiple passages through which a fluid agent may exit the distalend of elongated medical device 20.

Opening 56 is provided as a sealing passage that forms a fluid-tight orfluid-resistant seal around an elongated member or device passing therethrough to prevent the back flow of blood or other body fluids intoelongated body lumen 23. Alternatively opening 56 may be provided as anopen passage that does not resist the back flow of body fluids into bodylumen 52.

It is recognized that in some applications, passage of a device or fluidagent through tracking member 30 may be unnecessary. In correspondingembodiments, tracking member 30 may be provided without opening 56 or asa solid member, without lumen 54.

In any of the various embodiments described herein, tracking member 30,or any portion thereof, may be provided as a drug-eluting member. A drugeluting portion 39 may be formed from or coated with a polymericmaterial adapted for doping with a pharmacological or biological agent,such as a steroid or other anti-inflammatory or an antibiotic agent,intended for elution into the body tissue or body fluids at the implantsite. Methods for incorporating a drug in a medical lead for elutionafter implantation are known in the art. Reference is made, for example,to U.S. Pat. No. 5,265,608, incorporated herein by reference in itsentirety.

FIG. 6 is a schematic diagram of a helical fixation member and atracking member according to an embodiment of the present invention. Asillustrated in FIG. 6, a helical fixation member 60 according to anembodiment of the present invention includes a fixed diameter 66 acrossproximal windings 64 such that proximal windings 64 are supported ontheir inner diameter by tracking member 30. Proximal winding diameter 66is approximately equal to the outer dimension of tracking member 30.Distal windings 68 of helical fixation member 60 are formed with adiameter 70 that is larger than the outer diameter of fixation member 30so that tracking member 30 is spaced distance 36 from helical fixationmember 60 to form a tissue engaging gap, as described above. Thus,according to an embodiment of the present invention, helical fixationmember 32 is formed with a step increase in winding diameter so as to becorrespondingly spaced from fixation member 60. The step increase inwinding diameter may occur anywhere along helical fixation memberproximal to tissue-piercing tip 62.

The proximal windings 64 having a smaller winding diameter create aphysical stop against body tissue engaged in space 36. As helicalfixation member 32 is rotated into implant site tissue, torsionalresistance will increase as the tissue engaged in the gap formed bydistance 36 between fixation member 60 and tracking member 30 reachesthe smaller proximal windings, thereby providing tactile feedback to aclinician that fixation member 32 is fixated in the tissue.

In FIG. 6, the distal portion of the final distal winding 72 is showncanted at an angle 74 relative to the normal pitch of distal windings68, causing distal tip 62 of helical fixation member 60 to be angledmore toward the distal end 38 of tracking member 30. In someembodiments, a canted distal tip 34 is provided so that upon rotation ofthe elongated medical device, tissue-piercing distal tip 62 readilyengages and enters the body tissue at the implant site. Tissue-piercingdistal tip 62 can be provided with a beveled or sharpened edge to easeentry into the tissue.

Other variations in the spatial arrangement of tissue piercing distaltip 62 relative to the remainder of helical fixation member 60 andtracking member 30 may be provided to facilitate engagement and entry oftissue-piercing distal tip 62 into a targeted tissue. FIG. 7A is an endview of an elongated medical device illustrating one configuration ofthe tissue-piercing distal tip of the helical fixation member accordingto an embodiment of the present invention. Tracking member 30 is shownextending through helical fixation member 60 spaced distance 36 fromtracking member 60 along at least a distal portion of helical fixationmember 60. The final distal winding 80 of helical fixation member 60 isshown having a non-concentric winding diameter causing distal tip 62 ofhelical fixation member 60 to extend outward an additional distance 82from tracking member 30.

Upon rotation of the elongated medical device, distal tip 62 will piercethe tissue at the implant site. The outward extension of distal tip 62created by the non-concentric winding diameter of distal winding 80facilitates engagement and entry of tip 62 into body tissue at theimplant site, for example into a cardiac vein wall. In particularapplications, the relation of tissue-piercing distal tip 62 relative tothe winding diameter and pitch of helical fixation member 60 andrelative to the tracking member 30 may vary in order to enhance theengagement and entry of distal tip 62 into body tissue at a targetedimplant site upon rotation of the elongated medical device.

Distance 36 may or may not be uniform in cross-section. For example,according to an embodiment of the present invention, tracking member 30may be provided with a generally circular cross-section as shown in FIG.7A so that distance 36 between fixation member 60 and tracking member 30is generally symmetrical around tracking member 30. However, in someembodiments, a tracking member may be provided with a non-circularcross-section to form a generally non-symmetrical or non-uniformdistance 36 between fixation member 60 and tracking member 30. FIG. 7Bis an end view of a tracking member 31 according to an embodiment of thepresent invention having a non-circular cross-section resulting in anon-uniform distance 36′ between fixation member 60 and tracking member31. Such a non-uniform distance 36′ results in greater penetration offixation member 32 on one side of tracking member 31 than on the other.Preferentially greater penetration of helical fixation member 60 in agiven direction at the implant site may allow more optimal fixation in atargeted tissue for a particular therapy delivery. For example, in thecardiac vein application, deeper penetration into the left ventricularmyocardium may be desired with less penetration on the outer surface ofthe cardiac vein. Preferentially greater penetration of helical fixationmember 60 in a given direction at the implant site may also allow adelicate anatomical feature to be avoided, such as a nerve or artery,while still allowing secure fixation of helical fixation member 60.Non-circular tracking member 31 is shown having a generally “D” shapedgeometry, however, it is appreciated that a tracking member may beprovided with a variety of cross-sectional geometries without departingfrom the scope of the invention.

FIGS. 8, 9 and 10 illustrate alternative configurations of a helicalfixation member and corresponding tracking member for creating atissue-engaging space there between. In FIG. 8, distance space 36between tracking member 30 and fixation member 80 is created byfabricating helical fixation member 80 with a variable winding diameter82 that increases in the direction of tissue-piercing distal tip 84. Thevariable winding diameter 82 is continuously increasing so that distance36 that the distal windings of helical fixation member 80 are spacedfrom tracking member 30 increases from the proximal end of the distalwindings to the distal end of the distal windings.

Upon rotation of the elongated medical device, tissue-piercing distaltip 84 enters the tissue at the implant site and helical fixation memberbecomes fixed within the targeted tissue. A layer of tissue will beengaged within the gap formed by distanced 36 between tracking member 30and fixation member 80. As fixation member 80 is advanced further intothe implant site tissue, greater resistance will be met as the gapformed by distance 36 between tracking member 30 and fixation member 80becomes smaller adjacent proximal windings of helical fixation member80. The increasing resistance provides tactile feedback to an implantingclinician that the helical fixation member is engaged with the tissue atthe implant site.

FIG. 9 is a schematic diagram of a helical fixation member and trackingmember according to an embodiment of the present invention. Asillustrated in FIG. 9, according to an embodiment of the presentinvention, helical fixation member 32 is provided with a constantwinding diameter, while tracking member 90 is provided with a taperedgeometry. The outer diameter of tracking member 90 decreases movingtoward distal end 92 of tracking member 90 creating a variation indistance 36 between helical fixation member 32 and tracking member 90.

As illustrated in FIG. 10, according to an embodiment of the presentinvention, tracking member 94 is formed having a fixed outer diameteralong a proximal portion 96 and a tapering or decreasing diameter alonga distal portion 97. Helical fixation member 32 is provided with aconstant winding diameter thereby creating a tissue-engaging gapcorresponding to distance 36 along the tapering, distal portion 97 oftracking member 94. In alternative embodiments, the tracking member 94may be provided with a step-wise decrease in diameter at any point alongits length proximal to the tissue-piercing distal tip of the helicalfixation member 32 to create a tissue-engaging gap corresponding todistance 36 between a distal portion of helical fixation member 32 andthe tracking member 94.

It is recognized that numerous configurations of a helical fixationmember and a corresponding tracking member extending there through canbe conceived for creating a tissue-engaging space between the fixationmember and the tracking member beginning at the tissue-piercing distaltip of the fixation member and extending proximally from the tip for atleast a portion of the length of the fixation member. As such, the scopeof the invention is not intended to be limited to the specificconfigurations shown in the accompanying drawings. Indeed, thetissue-engaging gap formed by distance 36 may be constant or variable incross-section moving proximally from the tissue-piercing distal tip ofthe fixation member. Associated geometries of a helical fixation memberand associated tracking member for forming a tissue-engaging space therebetween may include constant or variable dimensions, which change in agradual or step-wise manner, as illustrated by the example embodimentsshown in FIGS. 5 through 10.

Welding sleeve 76 is shown in FIG. 10 with a proximal undercut groove 77and distal undercut groove 77′ extending from the channel 79 providedfor holding tracking member 94. Proximal undercut groove 77 promotesstability of the mechanical coupling between tracking member 94 andwelding sleeve 76 when forces are exerted against tracking member distalend 96. Distal undercut groove 77′ promotes stability of the mechanicalcoupling between tracking member 94 and welding sleeve 76 when forcesare exerted against proximal face 78 of tracking member 94. Forces maybe exerted against proximal face 78 when an elongated member such as aguide wire, stylet, microcatheter or needle is advanced through bodylumen 23. Proximal face 78 is shown chamfered to promote unobstructedadvancement of an elongated member through lumen 23 into tracking memberlumen 54 and out passage 98 at tracking member distal end 96. It isrecognized that welding sleeve 76 may be designed with varyinggeometries to promote a stable mechanical coupling between weldingsleeve 76 and tracking member 94.

FIG. 11 is a plan view of a medical electrical lead according to anembodiment of the present invention. As illustrated in FIG. 11,according to an embodiment of the present invention, lead 100 includesan elongated lead body 102 having helical fixation member 32 extendingfrom distal lead body end 104. Tracking member 30 extends throughhelical fixation member 32 as described above. Lead 100 is provided withone or more electrodes for use in sensing electrical body signals and/ordelivering an electrical stimulation therapy. Lead 100 is shown havingmultiple ring electrodes 108, 110 and 112 and a coil electrode 114. Inaddition, helical fixation member 32 may serve as an electrode.Electrodes 108, 110, 112, and 114 and fixation member 32 are coupled toinsulated conductors extending from each corresponding electrode toproximal lead end 106 for electrical coupling to a connector assembly116 according to arrangements and methods known in the art.

In some embodiments, helical fixation member 32 and one or more of ringelectrodes 108, 110 and 112 may be configured in a multi-cathodalarrangement. Each of fixation member 32 and electrodes 108, 110, and 112are coupled to separate, insulated conductors and can be selectivelycoupled to circuitry included in an associated medical electricalstimulation device. As such, if the sensing or stimulation performanceobtained using, for example, fixation member 32 is unacceptable, one ofelectrodes 108, 110 or 112 may be selected to achieve better leadperformance. In other embodiments, electrodes 108, 110 and 112 andfixation member 32 may be configured in any bi-polar or multi-polarelectrode arrangement. Electrode selection for sensing and/orstimulation is performed using switching circuitry 9 (shown in FIG. 1)included in an associated therapy/monitoring device.

In one particular example in which lead 100 is used as cardiac veinlead, one or more electrodes 108, 110 and 112 and helical fixationmember 32 may be provided as selectable cathode electrodes. In someinstances, undesired phrenic nerve stimulation occurs when pacing pulsesare delivered to the left ventricle of the heart using a cardiac veinlead. When lead 100 is implanted in a cardiac vein and fixed at adesired implant site using helical fixation member 32, phrenic nervestimulation that may occur using one of fixation member 32 or electrodes108, 110, or 112 may be avoided by selecting a different one of fixationmember 32 or electrodes 108, 110, or 112 as an alternative cathodeelectrode.

Lead 100 is also shown to include coil electrode 114. Coil electrode 114is typically used for high-voltage stimulation applications such as fordelivering a cardioversion or defibrillation shock to a patient's heart.Coil electrode 114 may alternatively be used for sensing and/orlow-voltage stimulation application in combination with any of the otherelectrodes 108, 110 and 112 or fixation member 32 carried by lead 100 orany other electrodes included in an implanted lead system. It isappreciated that in various embodiments, lead 100 may be equipped withother types of electrodes or physiological sensors.

FIG. 12 illustrates a method for deploying elongated medical device 20.In this example, elongated medical device 20 is embodied as a coronarysinus lead as shown previously in FIG. 1. Medical device 20 is deployedto a cardiac vein location with the use of a guide wire 120. Similarguide wire assisted procedures may be used for deployment of anelongated medical device in other body locations. In an implantationprocedure, guide wire 120 is advanced to a desired implant site. In theexample shown in FIG. 12, guide wire 120 is advanced via the coronarysinus to a desired implant site in a cardiac vein 124, over the leftventricle. Elongated medical device 20 is advanced to the implant siteby advancing device 20 over the guide wire 120. Elongated medical device20 may also be deployed with the use of a guide catheter.

FIG. 13A is an enlarged view of the elongated medical device 20 beingadvanced into a cardiac vein 124 over guide wire 120. As elongatedmedical device 20 is advanced over guide wire 120, device 20 iscounter-rotated as indicated by arrow 130 to prevent tissue-piercingdistal tip 34 of helical fixation member 32 from snagging or catching ontissue or anatomical structures along the implantation pathway.Elongated medical device body 22 is provided with a torsional stiffnessadequate to transfer rotational motion from the proximal end 24 (shownin FIG. 2) to the distal end 26 of elongated medical device 20. Trackingmember 30 extending distally from helical fixation member 32, promotesthe safe passage of helical fixation member 32 along the implantpathway.

Tracking member 30 is provided as a flexible member for tracking theguide wire 120 to the implant site while protecting helical fixationmember 32 from catching or snagging on tissue as device 20 is advanced.When welding sleeve 44 (shown in FIG. 5) is used in assembling elongateddevice 20, welding sleeve 44 creates a relatively stiff segment neardistal end 26 of elongated body 22. The stiff segment near distal end 26associated with a relatively rigid welding sleeve assembly may not trackwell along a tortuous implantation pathway. By providing tracking member30 as a flexible member, elongated medical device 20 can be passed overa guide wire and follow a tortuous pathway to an implant site.

Tracking member 30 may be formed having a variable stiffness optimizedfor flexibly tracking a tortuous implantation pathway and promotingsmooth advancement over a guide wire while protecting helical fixationmember 32 from becoming caught on body tissue or anatomical structuresand thereby causing tissue injury or becoming damaged or distorted. Arelatively more flexible distal end 38 of tracking member 30 can help toprevent buckling of tracking member 30 over guide wire 120 as elongatedmedical device 20 is advanced over guide wire 120. Greater flexibilitynear tracking member distal end 38 improves the ability to maneuvertracking member 30 into selected vein branches.

FIG. 13B illustrates fixation of the elongated medical device 20 at thetargeted implant site in vein 124. After advancing device 20 to atargeted implant site, fluoroscopic imaging, electrophysiologicalmeasurements or other testing may be performed to verify acceptablepositioning of elongated medical device 20. In some embodiments, aradio-opaque or other imaging contrast solution 140 may be injectedthrough the lumen 23 (shown in FIG. 5) of elongated medical device 20out distal tracking member passage 56 to allow visualization andverification of the anatomical location of tracking member 30 andhelical fixation member 32.

Once elongated medical device 20 is positioned at the targeted implantsite, device 20 is rotated at its proximal end in the directionindicated by arrow 132 to cause tissue-piercing distal tip 34 to engageand enter the wall of vein 124. Fixation of helical fixation member 32is achieved by further rotation of elongated medical device 20 indirection 132. The wall of vein 124 will become engaged in the gapformed by distance 36 between tracking member 30 and helical fixationmember 32. As helical fixation member 32 becomes fixed within the wallof vein 124, torsional resistance will increase and be transferred alongelongated medical device body 22 from distal end 26 to the proximal endof elongated medical device 20. The transfer of increasing torsionalresistance provides tactile feedback to the implanting clinician,indicating fixation of helical fixation member 32 in body tissue. Uponverification of acceptable implantation of the distal end 26 of medicaldevice 20, guide wire 120 can be withdrawn and removed from device 20.

Injection of an imaging contrast agent 140 can be also be used to verifyfixation of helical member 32. Injection of a radio-opaque contractsolution causes residual staining of the tissue engaged in the gapformed by distance 36. As such, visualization of the residual stainingof engaged tissue under fluoroscopy can be used to verify fixation ofhelical member 32. Contrast agent 140 can be flushed away by injectingsterile saline through elongated body lumen 23 after imaging iscompleted.

FIG. 14 is a plan view of a stylet that may be used in combination withan elongated medical device. Stylet 150 is provided with an elongatedbody 156 with a preformed bend or angle 158. Angle 158 is located adistance 159 from distal end 160 of stylet 150 that is slightly greaterthan the “stiff” distal segment of the corresponding elongated medicaldevice corresponding to the location of a welding assembly. Stylet 150is provided with a proximal handle 152. Handle 152 is provided with amarker 154, which may be a physical or printed feature on handle 152, toindicate the plane of angle 158. As shown in FIG. 14, marker 154 is aradial protrusion extending from handle 152 in the plane correspondingto angle 158.

FIG. 15A is a sectional view of elongated medical device 20 showingstylet 150 fully inserted in device 20. Pre-formed angle 158 causeselongated medical device 20 to bend at a location proximal to therelative stiff distal segment corresponding to welding sleeve 44.Distance 159 between preformed angle 158 and stylet distal end 160 isdesigned to cause elongated medical device 20 to bend at flexibleportion of body 22. Stylet body 156 is formed with a diameter greaterthan the diameter of tracking member lumen 54 such that the proximalface 78 of tracking member 30 interfaces with stylet distal end 160,acting as a mechanical stop to prevent over-advancement of stylet 150into device 20.

Marker 154 indicates to an implanting clinician the direction thattracking member 30 is directed when stylet 150 is fully inserted inelongated medical device 20. Thus stylet 150 can be used to facilitatesteering of elongated medical device along a desired implant pathway.For example, use of stylet 150 may facilitate sub-selection of cardiacveins when advancing elongated medical device 20 to a desired cardiacvein implant site. A set of stylets could be provided, each having apre-formed angle of a different degree, to facilitate maneuvering ofelongated medical device 20 around different angles, bends or otherobstructions encountered along an implantation pathway.

Moreover, stylet 150 can be used to direct tissue-piercing distal tip 34of helical fixation member 32 toward targeted tissue at an implant site.In the example of the cardiac vein implant site, angle 158 may bepositioned to preferentially direct tissue-piercing distal tip 34 intothe myocardium.

FIG. 15B is a sectional view of the distal portion of elongated medicaldevice 20 provided with a solid tracking member 170. In applicationsthat do not require passing an elongated member out the distal end 172of tracking member 170, tracking member 170 can be provided as a solidmember, without a distal passage. Stylet 150 is advanced up to proximalend 174 of tracking member 170 to facilitate steering of tracking member170 around obstacles and orienting tissue-piercing distal tip 34 towarda targeted implant site. Elongated device 20 may be implanted with theaid of a guide catheter 180. The use of a guide catheter for steeringcatheters or leads to a targeted internal body site is known in the art.

FIG. 16 is a sectional view of elongated medical device 20 and amicrocatheter for use in local administration of a fluid agent.Microcatheter 200 can be advanced through elongated device body lumen23, through tracking member lumen 54, and out distal end 38 of trackingmember 30 through passage 56. The proximal end 204 of microcatheter 200is adapted to accept injection, manually or with the use of a pump, of afluid agent 206 from a fluid reservoir. Fluid agent 206 which may be,for example, a pharmacological, biologic or genetic agent or an imagingcontrast agent. Fluid agent 206 exits microcatheter distal end 202.Elongated medical device 20 may thus be used in local delivery of afluid agent for therapeutic or imaging purposes.

An elongated medical device has been presented in the foregoingdescription with reference to specific embodiments. It is appreciatedthat various modifications to the referenced embodiments may be madewithout departing from the scope of the invention as set forth in thefollowing claims.

1. A medical electrical lead comprising: an elongated body having aproximal end and a distal end; a helical fixation member extending fromthe distal end of the elongated body, the helical fixation member havinga distal tip for fixedly engaging the distal end of the elongated bodyat an implant site, and a tracking member extending from the distal endof the elongated body and extending through the helical fixation memberand outward from the distal tip of the helical fixation member, whereinthe tracking member having a proximal portion extending out from theelongated body distal end having an outer diameter, and the helicalfixation member having a corresponding proximal portion extending outfrom the elongated body distal end; and wherein the helical fixationmember includes a first winding diameter along a proximal portion of thehelical fixation member extending from the elongated body distal end anda second winding diameter, greater than the first winding diameter,along a distal portion of the helical fixation member, a tissue engaginggap extending along the second winding diameter of the distal portion ofthe helical fixation member, the helical fixation member proximalportion having the first winding diameter forming a mechanical stop forresisting further advancement of the helical fixation member into thetissue.
 2. The medical electrical lead of claim 1, wherein the trackingmember includes a substantially circular cross-section.
 3. The medicalelectrical lead of claim 1, wherein the tracking member is adrug-eluting member.
 4. The medical electrical lead of claim 1, whereinthe helical fixation member is formed having a winding pitch and thedistal tip of the helical fixation member is canted with respect to thewinding pitch
 5. The medical electrical lead of claim 1, wherein theelongated body includes a lumen extending from the proximal end of theelongated body to the distal end of the elongated body to receive one ofan elongated member and a fluid and the tracking member comprises alumen in communication with the elongated body lumen.
 6. The medicalelectrical lead of claim 1, wherein the elongated member is a stylethaving a preformed angle to control an orientation of the trackingmember.
 7. The medical electrical lead of claim 6, wherein the elongatedmember is a stylet having a preformed angle to control an orientation ofthe distal tip of the helical fixation member toward the implant site.8. The medical electrical lead of claim 1, wherein the predetermineddistance being about constant along a linear portion of the helicalfixation member extending proximally from the helical fixation memberdistal tip.
 9. A medical electrical lead comprising: an elongated bodyhaving a proximal end and a distal end; a helical fixation memberextending from the distal end of the elongated body, the helicalfixation member having a distal tip for fixedly engaging the distal endof the elongated body at an implant site, and a tracking memberextending from the distal end of the elongated body and extendingthrough the helical fixation member and outward from the distal tip ofthe helical fixation member, wherein the tracking member having aproximal portion extending out from the elongated body distal end havingan outer diameter, and the helical fixation member having acorresponding proximal portion extending out from the elongated bodydistal end; and wherein the helical fixation member includes a finalwinding adjacent the distal tip and at least one proximal winding, thefinal winding and the at least one proximal winding beingnon-concentric.
 10. A medical electrical lead comprising: an elongatedbody having a proximal end and a distal end; a helical fixation memberextending from the distal end of the elongated body, the helicalfixation member having a distal tip for fixedly engaging the distal endof the elongated body at an implant site, and a tracking memberextending from the distal end of the elongated body and extendingthrough the helical fixation member and outward from the distal tip ofthe helical fixation member, wherein the tracking member haying aproximal portion extending out from the elongated body distal end havingan outer diameter, and the helical fixation member having acorresponding proximal portion extending out from the elongated bodydistal end; and wherein the tracking member is formed having a D-shapecross-section.
 11. An implantable medical device system, comprising: anelongated body having a proximal end and a distal end; a helicalfixation member extending from the distal end of the elongated body, thehelical fixation member having a distal tip for fixedly engaging thedistal end of the elongated body at an implant site, and a trackingmember extending from the distal end of the elongated body and extendingthrough the helical fixation member and outward from the distal tip ofthe helical fixation member, the tracking member including an outersurface and the helical fixation member including an inner surfaceadjacent to and spaced a predetermined distance from the outer surfaceof the tracking member to form a tissue engaging gap between the helicalfixation member and the tracking member for controlling a depth of bodytissue engaged in the tissue engaging gap at the implant site; andwherein the helical fixation member includes a first winding diameteralong a proximal portion of the helical fixation member extending fromthe distal end of the elongated body and a second winding diameter,greater than the first winding diameter, along a distal portion of thehelical fixation member.
 12. The device of claim 11, wherein thetracking member includes a first outer diameter along at least a distalportion of the helical fixation member and a second outer diameter alongother than the distal portion of the helical fixation member, the seconddiameter being greater than the first diameter.
 13. The device of claim11, wherein the tracking member includes a first portion having a firststiffness and a second portion having a second stiffness not equal tothe first stiffness.